For conventional optical lenses, particularly photochromic lenses, generally those using inorganic materials have spread. In other words, generally, a coating layer has been added to the surface of glass or a curable plastic such as CR-39 using an inorganic material having photochromic properties. Recently, plastic lenses having high impact resistance as lenses themselves have spread. Particularly, in the United States, lenses using polycarbonates spread widely, and the demand for sunglasses having impact resistance suitable for outdoor activities increases rapidly.
Conventionally, synthetic resin laminates having photochromic properties have been known including those obtained by adding a photochromic organic compound to a silicone-based surface curing coating material, applying the coating material to one surface of a laminate, followed by curing, and those obtained by adding a photochromic dye to a urethane-based coating material, applying the coating material to one surface of a synthetic resin laminate, followed by curing (Patent Document 1).
However, in the method of applying a coating material containing a photochromic dye to one surface of a synthetic resin laminate, the step of coating an individual laminate has been added, cracks have occurred due to the solvent in the coating component to cause poor appearance, and in addition it has also been difficult to limit the coated portion to only the desired portion, and there have been limitations in terms of product design.
Further, a method of direct kneading into a synthetic resin has been attempted, but a problem has been that due to the insufficient heat resistance of the photochromic dye during kneading, the decomposition and deterioration of the dye occur, causing insufficient exhibition of photochromic properties, and decreases in the physical properties of the synthetic resin laminate itself.
Patent Document 2 discloses a method of forming a synthetic resin laminate having photochromic properties in which two transparent resins are adhered with a polyurethane resin to which a photochromic dye is added. Patent Document 3 discloses a method of forming a lens by applying or transferring a resin layer having photochromic properties to a transparent plastic sheet and injection-molding a backup resin on the above resin layer. But, in the prior art, due to the problem of the low solubility of the photochromic dye, the thickness of the polyurethane resin layer having photochromic properties has increased in order to obtain sufficient contrast, and it has been difficult to perform control so that the layer is smooth and the thickness is uniform. The nonuniformity of thickness is exhibited as the unevenness of light and shade during coloring as it is, and therefore is not practically preferred. Further problems have been that delamination is likely to occur, and warpage occurs in the synthetic resin laminate due to the curing and shrinkage of the polyurethane resin.
In this manner, under present circumstances, a transparent synthetic resin laminate having photochromic properties that is good in coloring and excellent in the control of the surface smoothness of a coating of a layer having photochromic properties and the thickness of the coating is not obtained as a photochromic lens.